Conventionally, various dust-and-water proof structures for a casing are known wherein a casing having an internal space is split into two halves, and the fitting surfaces of the two casing halves are sealed so that dust or water droplets do not enter inside the casing. For example, Japanese Unexamined Patent Publication (Kokai) No. 2008-92096 discloses a structure to seal the fitting surfaces of two casing halves of an electronic device, such as a mobile phone handset, in order to prevent water from entering inside. Also, Japanese Unexamined Patent Publication (Kokai) No. 2002-111246 discloses a water proof structure for a device used outside. Since the dust proof function of a casing can be identical, to the water proof function, only a water proof structure will be explained below.
Japanese Unexamined Patent Publication (Kokai) No. 2008-92096 illustrates a water proof structure of a body casing of a foldable mobile phone handset. The foldable mobile phone handset is provided with a front casing member provided with operation key holes and a rear casing member, wherein a water proof packing, such as an O-ring made of rubber, is held between the fitting surfaces of both casings. The front casing member is provided with a groove at the fitting portion with the rear casing member, and the water proof packing is fitted in the groove. The rear casing member is provided with an elongated protrusion at the fitting portion with the front casing member. When the front casing member and the rear casing member are engaged, the elongated protrusion is inserted in the groove, so that the water proof packing fitted in the groove is compressed, to realize the water proof structure.
On the other hand, the casing described in Japanese Unexamined Patent Publication (Kokai) No. 2002-111246 comprises a cover and a casing body closed by the cover, wherein the casing body is provided on its upper end with a wall portion having a predetermined height, and inner peripheral surfaces of the casing body and the wall portion are continuous. The inner peripheral surface of the cover is fitted onto an outer peripheral surface of the wall portion. The overall length of an elastic packing held between the cover and the casing body is shorter than the overall circumference of the wall portion, and the elastic packing, when mounted, is stretched. Also, there is a recess inside the periphery of the cover, and when the cover and the casing body are engaged using screws, the elastic packing is compressed in the recess to provide a water proof structure.
Further, other than the water proof structures mentioned above, which use water proof packing or elastic packing, there is also known a water proof structure wherein one of the connecting surfaces of the two casings has a looped groove filled with a sealing agent, so that when the connecting surface is adhered to the connecting surface of the other casing half, water-tightness is established. Also, a structure is known, wherein after a sealing agent filled in the groove is cured, the sealing agent is compressed by the connecting surface of a mating casing half to seal.
However, in the water proof structures disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2008-92096 or in Japanese Unexamined Patent Publication (Kokai) No. 2002-111246, wherein a looped packing is used, the packing must be fitted in the groove or stretched to fit in the wall portion when the casing is assembled, thus leading to an increase of the number of assembly steps. Moreover, if the groove extends meanderingly, or the portion to which the packing is to be attached is three dimensional (cubic), it is necessary to deform and mount the packing in accordance with the shape of the groove, therefore, an operator must be highly skilled or very careful in assembling the casing, thus resulting in troublesome operations. In addition, the packing, if mounted twistedly, may fail to seal.
On the other hand, in the water proof structure using a sealing agent, the sealing function cannot be provided until the sealing agent is hardened, therefore, the assembling efficiency is reduced. Also, after the sealing agent is hardened, the connecting surfaces are adhered firmly to each other, therefore, it is necessary to destroy the sealed portion when the casing is disassembled for maintenance or repair, thus, it is inconvenient to repair or recycle the casing. Moreover, in the structure wherein the casing members are adhered to each other after the sealing agent filled in the groove is completely hardened, there is a possibility that an elastic deformation of the sealing agent occurs before it is hardened, and if such a deformation occurs, a dimensional deviation or positional displacement of the sealing agent may occur, thus leading to poor sealing performance.